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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"
"http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
<head>
<meta http-equiv="Content-Type" content="application/xhtml+xml; charset=UTF-8" />
<meta name="generator" content="AsciiDoc 9.0.0rc1" />
<title>The HAL-FORMS Media Type</title>
<style type="text/css">
/* Shared CSS for AsciiDoc xhtml11 and html5 backends */
/* Default font. */
body {
font-family: Georgia,serif;
}
/* Title font. */
h1, h2, h3, h4, h5, h6,
div.title, caption.title,
thead, p.table.header,
#toctitle,
#author, #revnumber, #revdate, #revremark,
#footer {
font-family: Arial,Helvetica,sans-serif;
}
body {
margin: 1em 5% 1em 5%;
}
a {
color: blue;
text-decoration: underline;
}
a:visited {
color: fuchsia;
}
em {
font-style: italic;
color: navy;
}
strong {
font-weight: bold;
color: #083194;
}
h1, h2, h3, h4, h5, h6 {
color: #527bbd;
margin-top: 1.2em;
margin-bottom: 0.5em;
line-height: 1.3;
}
h1, h2, h3 {
border-bottom: 2px solid silver;
}
h2 {
padding-top: 0.5em;
}
h3 {
float: left;
}
h3 + * {
clear: left;
}
h5 {
font-size: 1.0em;
}
div.sectionbody {
margin-left: 0;
}
hr {
border: 1px solid silver;
}
p {
margin-top: 0.5em;
margin-bottom: 0.5em;
}
ul, ol, li > p {
margin-top: 0;
}
ul > li { color: #aaa; }
ul > li > * { color: black; }
.monospaced, code, pre {
font-family: "Courier New", Courier, monospace;
font-size: inherit;
color: navy;
padding: 0;
margin: 0;
}
pre {
white-space: pre-wrap;
}
#author {
color: #527bbd;
font-weight: bold;
font-size: 1.1em;
}
#email {
}
#revnumber, #revdate, #revremark {
}
#footer {
font-size: small;
border-top: 2px solid silver;
padding-top: 0.5em;
margin-top: 4.0em;
}
#footer-text {
float: left;
padding-bottom: 0.5em;
}
#footer-badges {
float: right;
padding-bottom: 0.5em;
}
#preamble {
margin-top: 1.5em;
margin-bottom: 1.5em;
}
div.imageblock, div.exampleblock, div.verseblock,
div.quoteblock, div.literalblock, div.listingblock, div.sidebarblock,
div.admonitionblock {
margin-top: 1.0em;
margin-bottom: 1.5em;
}
div.admonitionblock {
margin-top: 2.0em;
margin-bottom: 2.0em;
margin-right: 10%;
color: #606060;
}
div.content { /* Block element content. */
padding: 0;
}
/* Block element titles. */
div.title, caption.title {
color: #527bbd;
font-weight: bold;
text-align: left;
margin-top: 1.0em;
margin-bottom: 0.5em;
}
div.title + * {
margin-top: 0;
}
td div.title:first-child {
margin-top: 0.0em;
}
div.content div.title:first-child {
margin-top: 0.0em;
}
div.content + div.title {
margin-top: 0.0em;
}
div.sidebarblock > div.content {
background: #ffffee;
border: 1px solid #dddddd;
border-left: 4px solid #f0f0f0;
padding: 0.5em;
}
div.listingblock > div.content {
border: 1px solid #dddddd;
border-left: 5px solid #f0f0f0;
background: #f8f8f8;
padding: 0.5em;
}
div.quoteblock, div.verseblock {
padding-left: 1.0em;
margin-left: 1.0em;
margin-right: 10%;
border-left: 5px solid #f0f0f0;
color: #888;
}
div.quoteblock > div.attribution {
padding-top: 0.5em;
text-align: right;
}
div.verseblock > pre.content {
font-family: inherit;
font-size: inherit;
}
div.verseblock > div.attribution {
padding-top: 0.75em;
text-align: left;
}
/* DEPRECATED: Pre version 8.2.7 verse style literal block. */
div.verseblock + div.attribution {
text-align: left;
}
div.admonitionblock .icon {
vertical-align: top;
font-size: 1.1em;
font-weight: bold;
text-decoration: underline;
color: #527bbd;
padding-right: 0.5em;
}
div.admonitionblock td.content {
padding-left: 0.5em;
border-left: 3px solid #dddddd;
}
div.exampleblock > div.content {
border-left: 3px solid #dddddd;
padding-left: 0.5em;
}
div.imageblock div.content { padding-left: 0; }
span.image img { border-style: none; vertical-align: text-bottom; }
a.image:visited { color: white; }
dl {
margin-top: 0.8em;
margin-bottom: 0.8em;
}
dt {
margin-top: 0.5em;
margin-bottom: 0;
font-style: normal;
color: navy;
}
dd > *:first-child {
margin-top: 0.1em;
}
ul, ol {
list-style-position: outside;
}
ol.arabic {
list-style-type: decimal;
}
ol.loweralpha {
list-style-type: lower-alpha;
}
ol.upperalpha {
list-style-type: upper-alpha;
}
ol.lowerroman {
list-style-type: lower-roman;
}
ol.upperroman {
list-style-type: upper-roman;
}
div.compact ul, div.compact ol,
div.compact p, div.compact p,
div.compact div, div.compact div {
margin-top: 0.1em;
margin-bottom: 0.1em;
}
tfoot {
font-weight: bold;
}
td > div.verse {
white-space: pre;
}
div.hdlist {
margin-top: 0.8em;
margin-bottom: 0.8em;
}
div.hdlist tr {
padding-bottom: 15px;
}
dt.hdlist1.strong, td.hdlist1.strong {
font-weight: bold;
}
td.hdlist1 {
vertical-align: top;
font-style: normal;
padding-right: 0.8em;
color: navy;
}
td.hdlist2 {
vertical-align: top;
}
div.hdlist.compact tr {
margin: 0;
padding-bottom: 0;
}
.comment {
background: yellow;
}
.footnote, .footnoteref {
font-size: 0.8em;
}
span.footnote, span.footnoteref {
vertical-align: super;
}
#footnotes {
margin: 20px 0 20px 0;
padding: 7px 0 0 0;
}
#footnotes div.footnote {
margin: 0 0 5px 0;
}
#footnotes hr {
border: none;
border-top: 1px solid silver;
height: 1px;
text-align: left;
margin-left: 0;
width: 20%;
min-width: 100px;
}
div.colist td {
padding-right: 0.5em;
padding-bottom: 0.3em;
vertical-align: top;
}
div.colist td img {
margin-top: 0.3em;
}
@media print {
#footer-badges { display: none; }
}
#toc {
margin-bottom: 2.5em;
}
#toctitle {
color: #527bbd;
font-size: 1.1em;
font-weight: bold;
margin-top: 1.0em;
margin-bottom: 0.1em;
}
div.toclevel0, div.toclevel1, div.toclevel2, div.toclevel3, div.toclevel4 {
margin-top: 0;
margin-bottom: 0;
}
div.toclevel2 {
margin-left: 2em;
font-size: 0.9em;
}
div.toclevel3 {
margin-left: 4em;
font-size: 0.9em;
}
div.toclevel4 {
margin-left: 6em;
font-size: 0.9em;
}
span.aqua { color: aqua; }
span.black { color: black; }
span.blue { color: blue; }
span.fuchsia { color: fuchsia; }
span.gray { color: gray; }
span.green { color: green; }
span.lime { color: lime; }
span.maroon { color: maroon; }
span.navy { color: navy; }
span.olive { color: olive; }
span.purple { color: purple; }
span.red { color: red; }
span.silver { color: silver; }
span.teal { color: teal; }
span.white { color: white; }
span.yellow { color: yellow; }
span.aqua-background { background: aqua; }
span.black-background { background: black; }
span.blue-background { background: blue; }
span.fuchsia-background { background: fuchsia; }
span.gray-background { background: gray; }
span.green-background { background: green; }
span.lime-background { background: lime; }
span.maroon-background { background: maroon; }
span.navy-background { background: navy; }
span.olive-background { background: olive; }
span.purple-background { background: purple; }
span.red-background { background: red; }
span.silver-background { background: silver; }
span.teal-background { background: teal; }
span.white-background { background: white; }
span.yellow-background { background: yellow; }
span.big { font-size: 2em; }
span.small { font-size: 0.6em; }
span.underline { text-decoration: underline; }
span.overline { text-decoration: overline; }
span.line-through { text-decoration: line-through; }
div.unbreakable { page-break-inside: avoid; }
/*
* xhtml11 specific
*
* */
div.tableblock {
margin-top: 1.0em;
margin-bottom: 1.5em;
}
div.tableblock > table {
border: 3px solid #527bbd;
}
thead, p.table.header {
font-weight: bold;
color: #527bbd;
}
p.table {
margin-top: 0;
}
/* Because the table frame attribute is overridden by CSS in most browsers. */
div.tableblock > table[frame="void"] {
border-style: none;
}
div.tableblock > table[frame="hsides"] {
border-left-style: none;
border-right-style: none;
}
div.tableblock > table[frame="vsides"] {
border-top-style: none;
border-bottom-style: none;
}
/*
* html5 specific
*
* */
table.tableblock {
margin-top: 1.0em;
margin-bottom: 1.5em;
}
thead, p.tableblock.header {
font-weight: bold;
color: #527bbd;
}
p.tableblock {
margin-top: 0;
}
table.tableblock {
border-width: 3px;
border-spacing: 0px;
border-style: solid;
border-color: #527bbd;
border-collapse: collapse;
}
th.tableblock, td.tableblock {
border-width: 1px;
padding: 4px;
border-style: solid;
border-color: #527bbd;
}
table.tableblock.frame-topbot {
border-left-style: hidden;
border-right-style: hidden;
}
table.tableblock.frame-sides {
border-top-style: hidden;
border-bottom-style: hidden;
}
table.tableblock.frame-none {
border-style: hidden;
}
th.tableblock.halign-left, td.tableblock.halign-left {
text-align: left;
}
th.tableblock.halign-center, td.tableblock.halign-center {
text-align: center;
}
th.tableblock.halign-right, td.tableblock.halign-right {
text-align: right;
}
th.tableblock.valign-top, td.tableblock.valign-top {
vertical-align: top;
}
th.tableblock.valign-middle, td.tableblock.valign-middle {
vertical-align: middle;
}
th.tableblock.valign-bottom, td.tableblock.valign-bottom {
vertical-align: bottom;
}
/*
* manpage specific
*
* */
body.manpage h1 {
padding-top: 0.5em;
padding-bottom: 0.5em;
border-top: 2px solid silver;
border-bottom: 2px solid silver;
}
body.manpage h2 {
border-style: none;
}
body.manpage div.sectionbody {
margin-left: 3em;
}
@media print {
body.manpage div#toc { display: none; }
}
</style>
<script type="text/javascript">
/*<+'])');
// Function that scans the DOM tree for header elements (the DOM2
// nodeIterator API would be a better technique but not supported by all
// browsers).
var iterate = function (el) {
for (var i = el.firstChild; i != null; i = i.nextSibling) {
if (i.nodeType == 1 /* Node.ELEMENT_NODE */) {
var mo = re.exec(i.tagName);
if (mo && (i.getAttribute("class") || i.getAttribute("className")) != "float") {
result[result.length] = new TocEntry(i, getText(i), mo[1]-1);
}
iterate(i);
}
}
}
iterate(el);
return result;
}
var toc = document.getElementById("toc");
if (!toc) {
return;
}
// Delete existing TOC entries in case we're reloading the TOC.
var tocEntriesToRemove = [];
var i;
for (i = 0; i < toc.childNodes.length; i++) {
var entry = toc.childNodes[i];
if (entry.nodeName.toLowerCase() == 'div'
&& entry.getAttribute("class")
&& entry.getAttribute("class").match(/^toclevel/))
tocEntriesToRemove.push(entry);
}
for (i = 0; i < tocEntriesToRemove.length; i++) {
toc.removeChild(tocEntriesToRemove[i]);
}
// Rebuild TOC entries.
var entries = tocEntries(document.getElementById("content"), toclevels);
for (var i = 0; i < entries.length; ++i) {
var entry = entries[i];
if (entry.element.id == "")
entry.element.id = "_toc_" + i;
var a = document.createElement("a");
a.href = "#" + entry.element.id;
a.appendChild(document.createTextNode(entry.text));
var div = document.createElement("div");
div.appendChild(a);
div.className = "toclevel" + entry.toclevel;
toc.appendChild(div);
}
if (entries.length == 0)
toc.parentNode.removeChild(toc);
},
/////////////////////////////////////////////////////////////////////
// Footnotes generator
/////////////////////////////////////////////////////////////////////
/* Based on footnote generation code from:
* http://www.brandspankingnew.net/archive/2005/07/format_footnote.html
*/
footnotes: function () {
// Delete existing footnote entries in case we're reloading the footnodes.
var i;
var noteholder = document.getElementById("footnotes");
if (!noteholder) {
return;
}
var entriesToRemove = [];
for (i = 0; i < noteholder.childNodes.length; i++) {
var entry = noteholder.childNodes[i];
if (entry.nodeName.toLowerCase() == 'div' && entry.getAttribute("class") == "footnote")
entriesToRemove.push(entry);
}
for (i = 0; i < entriesToRemove.length; i++) {
noteholder.removeChild(entriesToRemove[i]);
}
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<body class="article">
<div id="header">
<h1>The HAL-FORMS Media Type</h1>
<span id="author">Mike Amundsen</span><br />
<span id="email"><code><<a href="mailto:mca@amundsen.com">mca@amundsen.com</a>></code></span><br />
</div>
<div id="content">
<div class="sect1">
<h2 id="_status">Status</h2>
<div class="sectionbody">
<div class="dlist"><dl>
<dt class="hdlist1">
Doc Status
</dt>
<dd>
<p>
<strong><span class="white red-background">Working Draft</span></strong> — <em>Only experimental and ‘proof-of-concept’ apps should be built on this unstable draft.</em>
</p>
</dd>
<dt class="hdlist1">
Proposed IANA Registrations
</dt>
<dd>
<p>
<code>application/prs.hal-forms+json</code>
</p>
</dd>
<dt class="hdlist1">
Repository
</dt>
<dd>
<p>
<a href="https://github.com/rwcbook/hal-forms">https://github.com/rwcbook/hal-forms</a>
</p>
</dd>
<dt class="hdlist1">
Sample Implementation
</dt>
<dd>
<p>
<a href="https://github.com/apiacademy/ndcoslo2015/tree/hal-forms">https://github.com/apiacademy/ndcoslo2015/tree/hal-forms</a>
</p>
</dd>
<dt class="hdlist1">
Last Updated
</dt>
<dd>
<p>
2025-05-30
</p>
</dd>
</dl></div>
<div id="toc">
<div id="toctitle">Table of Contents</div>
<noscript><p><b>JavaScript must be enabled in your browser to display the table of contents.</b></p></noscript>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_summary">1. Summary</h2>
<div class="sectionbody">
<div class="paragraph"><p>This document describes a simple media type designed to add runtime FORM support for the <a href="#hal">[HAL]</a> media type. This is an <em>independent backward-compatible</em> extension of the HAL media type and MUST NOT be treated as standard HAL or as part of the HAL specification <a href="#hal-spec">[HALSPEC]</a>.</p></div>
<div class="sect2">
<h3 id="_motivation">1.1. Motivation</h3>
<div class="paragraph"><p>The HAL media type is a popular format for representing API responses. One of the possible reasons for this popularity is that HAL does not include detailed information about state transitions like filtered requests (e.g. search, sort, etc.) or write operations (e.g. create, edit, delete, etc.) as part of the specification. This feature keeps the complexity of HAL responses relatively low and easy to deal with. However, this also means one of the challenges of using HAL for APIs that support dynamic user inputs and/or varying work flow patterns is client applications must encode the detailed transition information (args, methods, work flow) directly in the client code. That means clients must be updated each time the input or work flow details change.</p></div>
<div class="paragraph"><p>The <strong>HAL-FORMS</strong> media type is an attempt to meet this challenge by creating a format and processing pattern to support dynamic UI forms for HAL responses. This is a backward-compatible, non-standard extension. There is nothing in this format or process pattern that adds breaking changes to the HAL media type itself. Clients that implement this extension can still be valid HAL clients by degrading gracefully (e.g. not throwing errors) when <strong>HAL-FORMS</strong> documents are not returned by the server.</p></div>
<div class="admonitionblock">
<table><tr>
<td class="icon">
<div class="title">Note</div>
</td>
<td class="content">
<div class="paragraph"><p>The <strong>HAL-FORMS</strong> media type design follows many of the HAL media type conventions. For this reason, <strong>HAL-FORMS</strong> "looks like HAL." However, it is important to keep in mind that <strong>HAL-FORMS</strong> is not the same as HAL — the two should not be thought of as interchangeable in any way. Finally, <strong>HAL-FORMS</strong> documents SHOULD always be sent over HTTP using the <code>application/prs.hal-forms+json</code> media type identifer.</p></div>
</td>
</tr></table>
</div>
</div>
<div class="sect2">
<h3 id="_updates">1.2. Updates</h3>
<div class="paragraph"><p>There is an open source repository <a href="#repo">[REPO]</a> for this specification. Readers are encouraged to submit updates via the repository any time.</p></div>
</div>
<div class="sect2">
<h3 id="_compliance">1.3. Compliance</h3>
<div class="paragraph"><p>An implementation (client or server) of this specification is not compliant if it fails to satisfy one or more of the MUST or REQUIRED elements. An implementation that satisfies all the MUST and REQUIRED elements as well as all the SHOULD and RECOMMENDED elements is said to be "unconditionally compliant"; one that satisfies all the MUST and REQUIRED elements but not all the SHOULD and RECOMMENDED elements is said to be "conditionally compliant."</p></div>
<div class="admonitionblock">
<table><tr>
<td class="icon">
<div class="title">Note</div>
</td>
<td class="content">
<div class="title">RFC2119 Words</div>
<div class="paragraph"><p>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD",
"SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be
interpreted as described in <a href="#rfc2119">[RFC2119]</a>.</p></div>
</td>
</tr></table>
</div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_the_hal_forms_media_type">2. The HAL-FORMS Media Type</h2>
<div class="sectionbody">
<div class="paragraph"><p>The <strong>HAL-FORMS</strong> media type is a simple JSON <a href="#rfc7159">[RFC7159]</a> document that contains information on the HTTP method, message content-type, and parameters to use when making a templated request to a HAL server. This media type can be used to provide dynamic state transition descriptions at runtime.</p></div>
<div class="sect2">
<h3 id="_example_hal_forms_document">2.1. Example HAL-FORMS document</h3>
<div class="paragraph"><p>Here is a simple <strong>HAL-FORMS</strong> document example:</p></div>
<div class="listingblock">
<div class="title">Example <strong>HAL-FORMS</strong> document.</div>
<div class="content">
<pre><code>{
"_links" : {
"self" : {
"href" : "http://api.example.org/rels/create"
}
},
"_templates" : {
"default" : {
"title" : "Create",
"method" : "POST",
"contentType" : "application/json",
"properties" : [
{"name" : "title", "required" : true, "value" : "", "prompt" : "Title", "regex" : "", "templated" : false},
{"name" : "completed", "required" : false, "value" : "false", "prompt" : "Completed", "regex" : ""}
]
}
}
}</code></pre>
</div></div>
</div>
<div class="sect2">
<h3 id="_the_hal_forms_media_type_identifier_string">2.2. The HAL-FORMS Media Type Identifier String</h3>
<div class="paragraph"><p>The media type identifier string for <strong>HAL-FORMS</strong> documents is: <code>application/prs.hal-forms+json</code> This SHOULD be used as part of the HTTP <code>accept</code> header when making a request for a <strong>HAL-FORMS</strong> document. It SHOULD appear as the HTTP <code>content-type</code> header when sending a response that contains a <strong>HAL-FORMS</strong> document.</p></div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_properties_of_a_hal_forms_document">3. Properties of a HAL-FORMS Document</h2>
<div class="sectionbody">
<div class="paragraph"><p>All <strong>HAL-FORMS</strong> documents MUST be valid JSON documents. A well-formed <strong>HAL-FORMS</strong> document has two top-level objects: <code>_links</code> and <code>_templates</code>. The following is a summary of the structure of the <strong>HAL-FORMS</strong> media type.</p></div>
<div class="sect2">
<h3 id="links-element">3.1. The <code>_links</code> Collection</h3>
<div class="paragraph"><p>The <code>_links</code> collection contains a dictionary collection of <code>link</code> elements associated with the <strong>HAL-FORMS</strong> document.</p></div>
<div class="sect3">
<h4 id="_code__links_code">3.1.1. <code>_links</code></h4>
<div class="paragraph"><p>Contains the collection of valid <code>link</code> elements in the <strong>HAL-FORMS</strong> document. This is a RECOMMENDED element. If this element is missing, is invalid, or cannot be parsed, the <strong>HAL-FORMS</strong> document SHOULD be treated as if it contains a <code>_links</code> collection which contains a single <code>link</code> element with the key of <code>self</code> and the value of the URL that was used to request the current <strong>HAL-FORMS</strong> document.</p></div>
<div class="paragraph"><p>Every <strong>HAL-FORMS</strong> document SHOULD have at least one <code>link</code> element in the collection with a <code>key</code> value set to <code>self</code>. The <code>_links</code> collection MAY have additional <code>link</code> elements with other <code>key</code> values. <strong>HAL-FORMS</strong> clients SHOULD ignore any <code>link</code> elements with <code>key</code> values they do not understand. Clients MAY reject a <strong>HAL-FORMS</strong> document that does not contain a <code>link</code> element with the <code>key</code> value set to <code>self</code>.</p></div>
</div>
<div class="sect3">
<h4 id="_code_link_code">3.1.2. <code>link</code></h4>
<div class="paragraph"><p>The <code>link</code> element consists of a key and a set of properties.</p></div>
<div class="ulist"><ul>
<li>
<p>
<code>key</code> : The unique identifier of the <code>link</code> element. This is a REQUIRED property for each <code>link</code> element. If this property is missing, is set to an unrecognized value, or cannot be parsed, the associated <code>link</code> element SHOULD be ignored.
</p>
</li>
<li>
<p>
<code>href</code> : The URL associated with the <code>key</code>. This is a REQUIRED property. If this is missing, set to empty or cannot be parsed, the associated <code>link</code> element SHOULD be ignored.
</p>
</li>
</ul></div>
<div class="admonitionblock">
<table><tr>
<td class="icon">
<div class="title">Note</div>
</td>
<td class="content">Additional properties MAY appear within a <code>link</code> element. <strong>HAL-FORMS</strong> clients SHOULD ignore any properties they do not understand and/or cannot parse.</td>
</tr></table>
</div>
</div>
</div>
<div class="sect2">
<h3 id="templates-element">3.2. The <code>_templates</code> Collection</h3>
<div class="paragraph"><p>The <code>_templates</code> collection describes the available state transition details including the HTTP method, message content-type, and arguments for the transition. This is a REQUIRED element. If the <strong>HAL-FORMS</strong> document does not contain this element or the contents are unrecognized or unparsable, the <strong>HAL-FORMS</strong> document SHOULD be ignored.</p></div>
<div class="paragraph"><p>The <code>_templates</code> element contains a dictionary collection of <code>template</code> objects. A valid <strong>HAL-FORMS</strong> document has at least one entry in the <code>_templates</code> dictionary collection. For this release, the only pre-defined key for those entries is <code>"default"</code>. If there is only one element in the collection the entry’s key SHOULD be set to <code>"default"</code>. If no <code>"default"</code> key is present, clients SHOULD assume the first element to be the default template. Clients MAY ignore additional entries in the collection. If this element is missing, set to empty or is unparsable, this template object SHOULD be ignored.</p></div>
<div class="paragraph"><p>Each <code>template</code> contains the following possible properties:</p></div>
<div class="sect3">
<h4 id="_code_contenttype_code">3.2.1. <code>contentType</code></h4>
<div class="paragraph"><p>The value of <code>contentType</code> is the media type the client SHOULD use when sending a request body to the server. This is an OPTIONAL element. The value of this property SHOULD be set to <code>"application/json"</code> or <code>"application/x-www-form-urlencoded"</code>. It MAY be set to other valid media-type values. If the <code>contentType</code> property is missing, is set to empty, or contains an unrecognized value, the client SHOULD act is if the <code>contentType</code> is set to <code>"application/json"</code>. See <a href="#encoding-request-bodies">Encoding Request Bodies</a> for details.</p></div>
</div>
<div class="sect3">
<h4 id="_code_method_code">3.2.2. <code>method</code></h4>
<div class="paragraph"><p>The HTTP method the client SHOULD use when the service request. Any valid HTTP method is allowed. This is a REQUIRED element. If the value is empty or is not understood by the client, the value MUST be treated as an HTTP GET.</p></div>
</div>
<div class="sect3">
<h4 id="_code_properties_code">3.2.3. <code>properties</code></h4>
<div class="paragraph"><p>An array of one or more anonymous <code>property</code> elements (see <a href="#property-element">The <code>property</code> Element</a>) that each describe a parameter for the associated state transition. This is an OPTIONAL element. If the array is missing or empty, the <code>properties</code> collection MUST be treated as an empty set of parameters — meaning that the transition is meant to be executed without passing any parameters.</p></div>
</div>
<div class="sect3">
<h4 id="_code_target_code">3.2.4. <code>target</code></h4>
<div class="paragraph"><p>Contains the identifier of the target URL for the client to use when submitting the completed HAL-FORMS template. For example, if the client should submit the completed template to the following URL: <code>http://api.example.org/jobs/</code> then the <code>target</code> proprety would be <code>target="http://api.example.org/jobs/"</code>.</p></div>
<div class="paragraph"><p>This is an OPTIONAL property. If this property is not understood by the recipient, left blank, or contains an invalid URL string, it SHOULD be ignored. In that case, the target URL for requests to be submitted is the <code>href</code> attribute of the <code>self</code> link contained in the <a href="#links-element"><code>_links</code> collection</a>. If neither a <code>target</code> is specified not a <code>self</code> link can be found, the template SHOULD be ignored.</p></div>
<div class="paragraph"><p>The <code>target</code> property holds the same information as the <a href="#htarget-query-string"><code>_htarget</code></a> query string property. If both the <code>target</code> prorperty and the <code>_htarget</code> query string value appear in the same message, the <code>_htarget</code> query string SHOULD be used and the <code>target</code> property SHOULD be ignored.</p></div>
</div>
<div class="sect3">
<h4 id="_code_title_code">3.2.5. <code>title</code></h4>
<div class="paragraph"><p>A human-readable string that can be used to identify this template. This is a valid JSON string. This is an OPTIONAL element. If it does not exist or is unparsable, consumers MAY use the <code>key</code> value of the template as the value for <code>title</code>.</p></div>
</div>
</div>
<div class="sect2">
<h3 id="property-element">3.3. The <code>property</code> Element</h3>
<div class="paragraph"><p>A JSON object that describes the details of the state transition element (<code>name</code>, <code>required</code>, <code>readOnly</code>, etc.). It appears as an anonymous array of <code>properties</code> as a child of the <code>_templates</code> element (See <a href="#templates-element">The <code>_templates</code> Element</a>).</p></div>
<div class="paragraph"><p>There is a set of <code>property</code> attributes that are considered <a href="#core-property-attributes"><em>core</em> attributes</a>. There are is also group of <code>property</code> attributes that are considered <a href="#additional-property-attributes"><em>additional</em> attributes</a>. Any library supporting the <strong>HAL-FORMS</strong> specification SHOULD support all of the core attributes and MAY support some or all of the additional attributes.</p></div>
<div class="sect3">
<h4 id="core-property-attributes">3.3.1. Core <code>property</code> Attributes</h4>
<div class="paragraph"><p>The core <code>property</code> attributes cover the basics of describing a single value used for a state transition (write or filter parameter). Most all attributes are OPTIONAL and MAY be ignored by <strong>HAL-FORMS</strong> processors. Below is a list of all the core <code>property</code> attributes.</p></div>
<div class="admonitionblock">
<table><tr>
<td class="icon">
<div class="title">Note</div>
</td>
<td class="content">
<div class="paragraph"><p>Any library, tooling, or utility supporting the <strong>HAL-FORMS</strong> specification SHOULD support all of the <em>core</em> <code>property</code> attributes.</p></div>
</td>
</tr></table>
</div>
<div class="sect4 xxx">
<h5 id="_code_name_code">3.3.1.1. <code>name</code></h5>
<div class="paragraph"><p>The <code>property</code> name. This is a valid JSON string. This is a REQUIRED element. If this attribute is missing or set to empty, the client SHOULD ignore this <code>property</code> object completely.</p></div>
</div>
<div class="sect4 xxx">
<h5 id="_code_prompt_code">3.3.1.2. <code>prompt</code></h5>
<div class="paragraph"><p>The human-readable prompt for the parameter. This is a valid JSON string. This is an OPTIONAL element. If this element is missing, clients MAY act as if the <code>prompt</code> value is set to the value in the <code>name</code> attribute.</p></div>
</div>
<div class="sect4 xxx">
<h5 id="_code_readonly_code">3.3.1.3. <code>readOnly</code></h5>
<div class="paragraph"><p>Indicates whether the parameter is read-only. This is a valid JSON boolean. This is an OPTIONAL element. If this element is missing, empty, or set to an unrecognized value, it SHOULD be treated as if the value of <code>readOnly</code> is set to ‘false’.</p></div>
</div>
<div class="sect4 xxx">
<h5 id="_code_regex_code">3.3.1.4. <code>regex</code></h5>
<div class="paragraph"><p>A regular expression string to be applied to the value of the parameter. Rules for valid values are the same as the HTML5 pattern attribute <a href="#html5pat">[HTML5PAT]</a>. This is an OPTIONAL element. If this attribute missing, is set to empty, or is unparseable , it SHOULD be ignored.</p></div>
</div>
<div class="sect4 xxx">
<h5 id="_code_required_code">3.3.1.5. <code>required</code></h5>
<div class="paragraph"><p>Indicates whether the parameter is required. This is a valid JSON boolean. This is an OPTIONAL element. If this attribute is missing, set to blank or contains an unrecognized value, it SHOULD be treated as if the value of <code>required</code> is set to ‘false’.</p></div>
</div>
<div class="sect4 xxx">
<h5 id="_code_templated_code">3.3.1.6. <code>templated</code></h5>
<div class="paragraph"><p>Indicates whether the <code>value</code> element contains a URI Template <a href="#rfc6570">[RFC6570]</a> string for the client to resolve. This is a valid JSON boolean. This is an OPTIONAL element. If this element is missing, set to empty, or contains unrecognized content, it SHOULD be treated as if the value of
<code>templated</code> is set to ‘false’.</p></div>
</div>
<div class="sect4 xxx">
<h5 id="_code_value_code">3.3.1.7. <code>value</code></h5>
<div class="paragraph"><p>The <code>property</code> value. This is a valid JSON string. This string MAY contain a URI Template (see <code>templated</code> for details). This is an OPTIONAL element. If it does not exist, clients SHOULD act as if the <code>value</code> property is set to an empty string.</p></div>
</div>
</div>
<div class="sect3">
<h4 id="additional-property-attributes">3.3.2. Additional <code>property</code> Attributes</h4>
<div class="paragraph"><p>The additional <code>property</code> attributes provide greater controls for describing the rendering and validation of input controls for a state transition (write and filter parameters). All of the additional attributes are OPTIONAL and one or more of them MAY be ignored by <strong>HAL-FORMS</strong> processors. Below is a list of all the additional <code>property</code> attributes.</p></div>
<div class="admonitionblock">
<table><tr>
<td class="icon">
<div class="title">Note</div>
</td>
<td class="content">
<div class="paragraph"><p>Any library, tooling, or utility supporting the <strong>HAL-FORMS</strong> specification MAY support some or all of the <em>additional</em> <code>property</code> attributes.</p></div>
</td>
</tr></table>
</div>
<div class="sect4 xxx">
<h5 id="_code_cols_code">3.3.2.1. <code>cols</code></h5>
<div class="paragraph"><p>The <code>cols</code> attribute specifies the expected maximum number of characters per line to display when rendering the input box. This attribute applies to the associated <code>property</code> element when that <code>property</code> element’s <code>type</code> attribute is set to <code>textarea</code>. The <code>cols</code> attribute is a non-negative integer greater than zero. If the <code>cols</code> attribute is missing or contains an invalid value, it can be assumed to be set to the value of <code>40</code>. If the <code>type</code> attribute of the associated <code>property</code> element is not set to <code>textarea</code>, this attribute SHOULD be ignored. This is an OPTIONAL attribute and it MAY be ignored. The <code>cols</code> attribute SHOULD appear along with the <code>rows</code> attribute.</p></div>
</div>
<div class="sect4 xxx">